I am opening this thread to begin listing selected forcing (radiative, sensitivities, and ocean heat content) factors unique to the Antarctic that may drive the potential collapse of the WAIS this century and which have not been fully accounted for by most current researchers in their current projections of ice mass loss contributions to SLR from the WAIS. I will start with the historical trends of antropogenic carbon dioxide emissions relative to various IPCC scenarios; which indicate that we are currently exceeding both SRES A1FI and RCP 8.5 (but currently a little bit below SRES A1B for carbon dioxide). Delaying getting such radiative forcing factors under control at an early date are critical to reduce the risk of abrupt ice mass loss from WAIS due to the thermal inertia of the oceans. It is important to note that all of the IPCC's statement about the risk of SLR are currently weighted by low emission scenarios such RCP 3 and 4.5, which the historical record indicates are not occurring and who probability of occurring become less with each passing day. If these unlikely low emission scenarios were weighted properly when evaluating the real risk of abrupt SLR the high emission scenarios such as SRES A1FI and RCP 8.5 would be given higher probabilities of occurrence. Also, the current high IPCC emission scenarios do not correctly account for the historical trends for methane and black carbon, nor for potential future high rates of radiative forcing from albedo changes, aerosol changes, and nature sources of methane and carbon dioxide such as the permafrost, and methane hydrates.

The accompanying figure from the HadGEM1 GCM predicts that 2011 radiative forcing from BC was almost twice that previously assumed by researchers while my next post will put the implications of this finding and the 2011 methane atmospheric concentrations into prospective.

The accompanying table corrects the published RCP 8.5 radiative forcing values for 2011 for both: (a) the Hadley calculated BC radiative forcing and for (b) the Shindell 2009 finding that direct and indirect aerosol effects change the ratio of methane's GWP to the IPCC 2007 assumed value from 105/72 = 1.46 over a 20-yr period together with the measured atmospheric methane concentration for 2011. These corrections/adjustments for indicated that in 2011 radiative forcing from GHG and BC together were at the levels assumed by RCP 8.5 to occur between 2018 and 2019. This is important because once initiated it will be impractical to slowdown the accelerating rate of ice mass loss from the WAIS.

Where the earth is currently with regard to radiative forcing is also important with regarding to combined equilibrium climate sensitivity and albedo as indicated by the attached figure from Hansen and Sato 2012, which indicates that as radiative forcing increases for a period the reduction in albedo resulting from such events as the loss of Arctic Sea Ice, and a decrease in winter snow cover, will significantly increase the climate sensitivity of the earth. Also note that while Hansen and Sato assume a fast feedback climate sensitivity of 3 C, a recent report from Fasullo and Trenberth, 2012, indicate that this fast feedback climate sensitivity is likely to be closer to 4.5 C rather than 3 C. While such assessments are not definitive, they do clearly identify a significant increase in the real risk of abrupt climate change (and associated abrupt SLR) as compared to the probabilities cited by the IPCC.

The accompanying figure from Kuhlbrot and McGregory 2012, shows the vertically integrated ocean heat uptake (OHU, which is significantly connected to upwelling) from El 0m to the ocean bottom. This figure illustrates both that: (a) the Southern Ocean dominates OHU (and thus the Southern Ocean is warming faster than any other ocean); and (b) the upwelling in the Bellingshausen, and Amundsen, Sea area are high which with time will deliver higher temperature CDW to the base of the glaciers adjoining these seas.

The accompanying figure from Manabe et al 1989, which illustrates a trend (from 1989 to 2059) to export heat flux from the tropics to the Southern Ocean from a simplified GCM subjected to a doubling of carbon dioxide (which following our current business as usual emission scenario should happen sometime after 2020). This illustrates (for a simplified model) how efficiently the ocean exports heat from the tropics to the Southern Ocean; which is helping to keep our average global surface temperature temporarily low (particularly during the past ten years of strong La Nina and weak El Nino events); but which is locking in now the continued rise of CDW temperatures that will help drive the probable collapse of the WAIS this century.

The accompanying figure from NOAA (Levitus et al) shows that while the rate of increase of the Ocean Heat Content, OHC, from 0 to 700m has slowed since about 2002, the rate of increase of OHC from 0 to 2000m has remained about constant; which implies that since about 2002 the rate of increase of OHC for from 700 to 2000m has accelerated. As much of this OHC from 700 to 2000m winds-up in the Southern Ocean, this trend clearly indicates that as compared to previous projections the CDW temperature in the WAIS may well increase faster than previous simplified models projected, probably due to increased ocean efficience in upwell (along the Pacific equator due to increase La Nina and neutral activity; and in the Southern Ocean due to strong winds and storm action). Note that some researchers have predicted that the increased La Nina and ENSO neutral conditions will remain more active for a while which is not good news for the WAIS.

In the accompanying figure I compare the ENSO Index (from NOAA) to UAH Satellite Temperatureof the Global Lower Atmosphere from 1979 to Jan. 2013. It should be noted that an ENSO Index of less than 1 is considered to be a neutral condition, thus since 2000 the world has been in either a La Nina or an ENSO neutral condition, which promotes upwelling in the Pacific equator contributing significantly to the somewhat flat rate of global lower atmospheric temperature rise since 2000. This is bad for at least two reasons: (a) as the Arctic atmosphere has warmed more rapidly than the topical atmosphere (partly because of the ENSO condition since 2000) this has lead more rapidly than previously project to a flattening of the thermal gradient from the Arctic to the equator which has allowed the jet stream to meander more than expected resulting in more blocking patterns and more extreme weather in the Northern Hemisphere (NH); and (b) as state previously this is driving more ocean heat content into the CDW around the Antarctic.

To emphasize the previous post I provide a figure from Climate Skeptic, where they corrected the global surface temperature record for both volcanic activity and ENSO effects, and what is left is an estimate of what the global surfaced temperature would have been without this fluctuations. This is important as the ENSO oscillates on a decadal scale from La Nina rich events to El Nino rich events; thus it can be expected that in the near future more El Nino events (with ENSO Index values greater than 1) will occur; and as indicated in my second image due to a shifting of the location of the Amundsen Sea Low, El Nino events tend to drive winds toward the Amundsen Sea Embayment (ASE) which inturn will drive more warm CDW into the ASE, which will inturn drive more warm CDW directly into the subglacial cavity that I posulate is already formed at the threshold of the Thwaites Glacier

The attached pdf of an article entitled "Tropical forcing of Circumpolar Deep Water Inflow and outlet glacier thinning in the Amundsen Sea Embayment, West Antarctica" by Steig et al 2012, discusses (in more detail than a single figure can provide) the probable interplay between tropical forcing from the Central Pacific Ocean to the thinning of outlet glaciers in ASE (and also the Bellingshausen Sea).

In the "Collapse" thread I noted that I developed a modified 95% Confidence Level, CL, RCP 8.5 Temperature projection assuming a significant increase of the methane concentration pathway beyond that assumed by the standard 95% CL RCP 8.5 scenario. This modified scenario assumes accelerated antropogenic use of shale gas and also the assumed natural methane emissions cited in the accompanying table. Although repeated in the "Collapse" thread the modified 95% CL RCP 8.5 Temperature projections are also attached here for convenience (see also the Forum section devoted to methane for background on this topic). It should also be noted here that as the methane concentration increases significantly in the atmosphere the chemical reactions that reduce methane to carbon dioxide are changed so as to significantly increase the GWP of methane (which is considered in this modified scenario).

To elaborate on one source of potentially high natural methane emissions, consider the first image that indicates Earth Sensitivity Model, ESM, projections of the increase in ocean heat transport in the Arctic Ocean, which indicates a major/abrupt increase by 2030; however as indicated early radiative forcing for combined anthropogenic GHG and BC is already at the 2019 level of RCP 8.5, thus it is likely that the surge of heat transport from the Atlantic into the Arctic could happen approximately 11 years from now, or 2024; which would trigger the accelerated release of methane from Arctic marine sediment hydrates. The second figure shows in panel: (a) Methane Distribution, (b) Methane Saturation Ratio, and (c) Background Methane Distribution of Methane Emitted from Marine Hydrate Decomposition in the 40th Year After Initiation Decomposition from Climate Change (which is probably around 2010) from SRES A1B, from Elliott et.al. 2011. Elliott et al's findings indicate that before 2050 large amounts of methane could be released from marine sediments worldwide with the preponderance coming from the Arctic Ocean particular after the expected surge of heat transport into the Arctic Ocean from the Atlantic around 2025.

Another important consideration with regard to the 98% CL risk of large emissions of methane and the risk of abrupt SLR from the potential collapse of the WAIS this century is the timing of when these large emissions begin. The previous post gives an idea of the timing an risk of methane emission from marine hydrates (focused on those from the Arctic Ocean and the East Siberian Arctic Shelf, ESAS, inparticular) for a GCM model for SRES A1B (and it is possible that the early introduction of warm North Atlantic currents into the Arctic Basin could accelerate the emission beyond the model projections). The first accompanying figure shows one emission scenario for carbon from the Northern Hemisphere permafrost (of which it is estimated that 2.7% will be methane, which for 100-yr GWP factor of 25 effectively increases the total GWP of the permafrost carbon emissions by over 50% from what they would have been if all of the emissions where carbon dioxide, this increases still more if a 100-yr GWP factor of 33 or a 20-yr GWP factor is used for the methane per Shindell et al. (2009)). However, the scenario for this cumulative carbon emission curve does not account for new findings that the rate of permafrost degradation is accelerated by UV light; nor by the "albedo flip" associated with the early loss of the Arctic Sea Ice (and the early season melting of snow cover above Arctic land); which the second figure from D. Lawrence (circa 2010) which shows a significant amplication of Arctic temperatures due to the "albedo flip" which would accelerate both carbon dioxide and methan emission from the permafrost.

While the accompanying figure about total potential fossil fuel sources for anthropogenic carbon emission from Hasen et al 2011, may not be news to most forum readers; I would like to point out that when the scenario for RCP 8.5 was being developed circa 2007, the anthropogenic carbon emission levels for RCP 8.5 were taken at a 90% value of published emission levels at that time. It is important to recognize that prior to 2007 most researchers assumed that commercially recoverable fossil fuels would limit anthropogenic carbon emissions to levels similar to RCP 8.5 (at a 90% available literature level); however, since 2007 unconventional fossil fuels have become commercial competitive indicating that RCP 8.5 should not be considered to be as unlikely as the IPCC states (particularly when adding the natural methane sources previously discussed with the anthropogenic emission levels now made possible both by unconventional fossil fuels but also by the dynamic economic growth of the Third World and of the continued population growth [particularly in Africa]). This all supports the use of both a 50% CL RCP 8.5 forcing for one WAIS collapse scenario (see the "Collapse" thread) and a modified 95% CL RCP 8.5 forcing for the other WAIS collapse scenario (note that based on the current world economic situation most informed sources [such as the World Bank] acknowledge that the lower IPCC forcing/emission scenarios are extremely unlikely and that unless serious economic changes are made to our business as usual behavior then RCP 8.5 is the path that we will continue on.

The accompanying figure from Levermann et al 2012, presents GCM projections of subsurface (ie upwelling CDW) ocean water temperatures in the various regions of the Antarctic, primarily for RCP 8.5. This is smoothed simplified projects and actual future values may fluctuate more and may increase more rapidly than assumed. Nevertheless, these projections indicate a significant expected increase in CDW temperatures around the WAIS before the end of the century according to RCP 8.5.

I am not sure that I have assembled this graph correctly, nevertheless: (a) note that the CDW temperature scale is plotted so that increasing water temperature is down; (b) for the CDW temperature note the change in the horizontal scale for the years from 1976 to 2012 compared to time after 2012; and (c) I tried to line-up the ENSO index for the years from 1992 to 2012. The main reasons to present this figure is: (a) to show the natural temperature fluctuations before 2012 and how they appear to line-up well with the ENSO index and that such fluctuations can be expected in the future [which may contribute to surges of ice mass loss in the ASE when the temperature fluctuations are on the high side]; and (b) to provide a comparison with the Levermann et al. temperatures for RCP 8.5 for the Amundsen Sea.

I just thought that I would provide this image of sea surface temperature anomalies, indicating that for the last month (austral summer) that the sea offshore of the ASE and Bellingshausen Seas have been abnormally high. While this is only one month, I think that if you go to the NOAA website you will see that more offer than not this anomolly is abnormally high very frequently.

For those not familar with how the SRES scenarios compare with the RCP scenarios, I provide the attached figure (which also includes some upgrading of the RCP scenarios based on the author's [Rogelj et al 2012, see attached pdf] study of climate sensitivity).

While there are many recently reported study finding warning about the temporary (many decades to a century) acceleration of GHG emissions from organic in the non-permafrost soil, but I found the following internet summary worth repeating here as a very probable positive feedback cause for accelerated radiative forcing this century:

"Earthworms may contribute to global warming: As environmentalists and politicians fret about man-made global warming, they may be ignoring another culprit: earthworms. According to a new study by an international team of researchers, earthworms could be contributing to global warming.The study looked at results from 237 separate experiments from published stories to explore earthworms’ role in affecting global warming. “Our results suggest that although earthworms are largely beneficial to soil fertility, they increase net soil greenhouse-gas emissions,” according to the study’s abstract.Worms affect how much carbon dioxide is produced in the soil and how much escapes into the atmosphere by altering the physical structure of the soil through burrowing, which makes it more porous. Earthworms interact with microbes in the soil that produce a large chunk of the carbon dioxide emissions.There are concerns that earthworms increase greenhouse gas emissions , which troubles scientists since earthworm numbers are on the rise.“Earthworms play an essential part in determining the greenhouse-gas balance of soils worldwide, and their influence is expected to grow over the next decades,’ reads the abstract. “They are thought to stimulate carbon sequestration in soil aggregates, but also to increase emissions of the main greenhouse gases carbon dioxide and nitrous oxide.”The study found that earthworms in soil increased nitrous oxide emissions by 42 percent and carbon dioxide emissions by 33 percent. However, the report also notes that worms can increase one type of greenhouse gas emissions while reducing another.The Guardian reports that approximately 20 percent of worldwide CO2 emissions and two-thirds of N2O emissions come from the soil — produced by natural biological processes involving plant roots, as well as the micro-organisms living in the ground."

While I have made this point previously, I would like to reiterate that the following quote from an internet summary for "Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods" by Gerald A. Meehl, Julie M. Arblaster, John T. Fasullo, Aixue Hu & Kevin E. Trenberth Nature Climate Change Vol:1, pp 360–364 (2011) doi:10.1038/nclimate1229; shows that for the past 10 years that a hiatus in strong El Nino events has: (a) accelerated the delivery of ocean heat content to the CDW in the Antarctic; and (b) when the hiatus ends soon the associated increase in global surface temperatures which will also (for a few years) increase the surface temperatures in the Antarctic Peninsula and the West Antarctic leading to such events as: (a) the likely collapse of the Larsen C ice shelf; and (b) an increased frequency of ice surface melt in the WAIS (which has been less frequent during the immediate past hiatus period):

"New analysis led by the National Center for Atmospheric Research (NCAR) suggests that the relative slowdown in global air temperature rises during the past decade may have been caused in part by the planet’s deep oceans.Scientists from NCAR and the Bureau of Meteorology in Australia claim that the oceans at times may absorb enough heat to flatten the rate of global warming for periods of as long as a decade even in the midst of longer-term warming.The study, based on computer simulations of global climate, points to ocean layers deeper than 1,000 feet (300 meters) as the main location of the “missing heat” during periods such as the past decade when global air temperatures showed little trend. The findings also suggest that several more intervals like this can be expected over the next century, even as the trend toward overall warming continues.NCAR’s Gerald Meehl, lead author of the study said: “We will see global warming go through hiatus periods in the future. However, these periods would likely last only about a decade or so, and warming would then resume. This study illustrates one reason why global temperatures do not simply rise in a straight line.”The research, by scientists at NCAR and the, was published online on September 18 in Nature Climate Change. Funding for the study came from the National Science Foundation, NCAR’s sponsor, and the Department of Energy.Where the missing heat goesThe 2000s were Earth’s warmest decade in more than a century of weather records. However, the single-year mark for warmest global temperature, which had been set in 1998, remained unmatched until 2010.Yet emissions of greenhouse gases continued to climb during the 2000s, and satellite measurements showed that the discrepancy between incoming sunshine and outgoing radiation from Earth actually increased. This implied that heat was building up somewhere on Earth, according to a 2010 study published in Science by NCAR researchers Kevin Trenberth and John Fasullo.The two scientists, who are coauthors on the new study, suggested that the oceans might be storing some of the heat that would otherwise go toward other processes, such as warming the atmosphere or land, or melting more ice and snow. Observations from a global network of buoys showed some warming in the upper ocean, but not enough to account for the global build-up of heat. Although scientists suspected the deep oceans were playing a role, few measurements were available to confirm that hypothesis.To track where the heat was going, Meehl and colleagues used a powerful software tool known as the Community Climate System Model, which was developed by scientists at NCAR and the Department of Energy with colleagues at other organizations. Using the model’s ability to portray complex interactions between the atmosphere, land, oceans, and sea ice, they performed five simulations of global temperatures.The simulations, which were based on projections of future greenhouse gas emissions from human activities, indicated that temperatures would rise by several degrees during this century. But each simulation also showed periods in which temperatures would stabilize for about a decade before climbing again. For example, one simulation showed the global average rising by about 2.5 degrees Fahrenheit (1.4 degrees Celsius) between 2000 and 2100, but with two decade-long hiatus periods during the century.During these hiatus periods, simulations showed that extra energy entered the oceans, with deeper layers absorbing a disproportionate amount of heat due to changes in oceanic circulation. The vast area of ocean below about 1,000 feet (300 meters) warmed by 18% to 19% more during hiatus periods than at other times. In contrast, the shallower global ocean above 1,000 feet warmed by 60% less than during non-hiatus periods in the simulation.“This study suggests the missing energy has indeed been buried in the ocean,” Trenberth says. “The heat has not disappeared, and so it cannot be ignored. It must have consequences.”A pattern like La NiñaThe simulations also indicated that the oceanic warming during hiatus periods has a regional signature. During a hiatus, average sea-surface temperatures decrease across the tropical Pacific, while they tend to increase at higher latitudes, especially around 30°S and 30°N in the Pacific and between 35°N and 40°N in the Atlantic, where surface waters converge to push heat into deeper oceanic layers.These patterns are similar to those observed during a La Niña event, according to Meehl. He adds that El Niño and La Niña events can be overlaid on top of a hiatus-related pattern. Global temperatures tend to drop slightly during La Niña, as cooler waters reach the surface of the tropical Pacific, and they rise slightly during El Niño, when those waters are warmer.“The main hiatus in observed warming has corresponded with La Niña conditions, which is consistent with the simulations,” Trenberth says."

I would also like to point out that not only has the recent hiatus in El Nino activity (see previous post) been masking (hiding) the rise in global surface temperatures for the past 10-years (thus reducing the atmospheric telecommunication of heat to the West Antarctic while increasing the ocean telecommunication of heat); similarly the melting of a large volume of Arctic sea ice for the past ten years has masked the Arctic amplification of the increase Arctic surface temperatures. Once the rate of Arctic sea ice volume loss decreases (in the next few years) the rate of increase of Arctic surface temperatures will accelerate thus further reducing the thermal gradient between the topics and the Arctic; which in turn will reduce the atmospheric telecommunication of energy from the tropics to the Arctic. Thus in a few years there will be more energy in the tropics (due both to the end of the El Nino hiatus and the drop in the rate of Arctic sea ice volume loss) to telecommunicate atmospherically to the West Antarctic (which as Steig et al have pointed out is the focus of such telecommunication from the Pacific tropics), which will likely result in the collapse of the Larsen C ice shelf by 2018 and the possible collapse of the thinned FRIS and/or RIS after 2070 due to the ice melt pond mechanism.

In regard to my postulated non-linear increase in the WAIS surface temperatures after 2070, I would like to add that: (a) much of the current 0.8 C/decade surface temperature rate of raise is driven by the warming of the Bellingshausen and Amundsen Sea, due to the upwelling of warm CDW in these areas, and due to the early austral spring retreat of ice extent in these areas (causing a 1.1 C/decade rise in the WAIS area during the austral spring); and (b) it is projected that the Antarctic sea ice we begin to deteriorate by 2070 particularly in the Weddell Sea area, which will then expose the previously insulated CDW in these areas to the atmosphere, which should drive up WAIS surface temperatures.

"Atmospheric concentrations of the three important greenhouse gases (GHGs) CO2, CH4 and N2O are mediated by processes in the terrestrial biosphere that are sensitive to climate and CO2. This leads to feedbacks between climate and land and has contributed to the sharp rise in atmospheric GHG concentrations since pre-industrial times. Here, we apply a process-based model to reproduce the historical atmospheric N2O and CH4 budgets within their uncertainties and apply future scenarios for climate, land-use change and reactive nitrogen (Nr) inputs to investigate future GHG emissions and their feedbacks with climate in a consistent and comprehensive framework1. Results suggest that in a business-as-usual scenario, terrestrial N2O and CH4 emissions increase by 80 and 45%, respectively, and the land becomes a net source of C by AD 2100. N2O and CH4 feedbacks imply an additional warming of 0.4–0.5 °C by AD 2300; on top of 0.8–1.0 °C caused by terrestrial carbon cycle and Albedo feedbacks. The land biosphere represents an increasingly positive feedback to anthropogenic climate change and amplifies equilibrium climate sensitivity by 22–27%. Strong mitigation limits the increase of terrestrial GHG emissions and prevents the land biosphere from acting as an increasingly strong amplifier to anthropogenic climate change."

It should be noted that none of this radiative forcing is included in any of the IPCC AR5 projections.

I thought that I would post this abstract:Mitigation of short-lived climate pollutants slows sea-level rise• Aixue Hu,1 • Yangyang Xu,2 • Claudia Tebaldi,1, 3 • Warren M. Washington1 • & Veerabhadran Ramanathan2 Nature Climate Change(2013)doi:10.1038/nclimate1869"Under present growth rates of greenhouse gas and black carbon aerosol emissions, global mean temperatures can warm by as much as 2 °C from pre-industrial temperatures by about 20501, 2. Mitigation of the four short-lived climate pollutants (SLCPs), methane, tropospheric ozone, hydrofluorocarbons and black carbon, has been shown to reduce the warming trend by about 50% by 2050. Here we focus on the potential impact of this SLCP mitigation on global sea-level rise (SLR). The temperature projections under various SLCP scenarios simulated by an energy-balance climate model1 are integrated with a semi-empirical SLR model3, derived from past trends in temperatures and SLR, to simulate future trends in SLR. A coupled ocean–atmosphere climate model4 is also used to estimate SLR trends due to just the ocean thermal expansion. Our results show that SLCP mitigation can have significant effects on SLR. It can decrease the SLR rate by 24–50% and reduce the cumulative SLR by 22–42% by 2100. If the SLCP mitigation is delayed by 25 years, the warming from pre-industrial temperature exceeds 2 °C by 2050 and the impact of mitigation actions on SLR is reduced by about a third."

I would like to note that instead of limiting methane and black carbon emissions, these are both actually increasing; thus I would expect an acceleration of SLR due to the greater short-term forcing from SLCP.

"The effect of enhanced plant gas emissions on climate is small on a global scale – only countering approximately 1 percent of climate warming, the study suggested. “This does not save us from climate warming,” says Paasonen. However, he says, “Aerosol effects on climate are one of the main uncertainties in climate models. Understanding this mechanism could help us reduce those uncertainties and make the models better.” The study also showed that the effect was much larger on a regional scale, counteracting possibly up to 30% of warming in more rural, forested areas where anthropogenic emissions of aerosols were much lower in comparison to the natural aerosols. That means that especially in places like Finland, Siberia, and Canada this feedback loop may reduce warming substantially.The researchers collected data at 11 different sites around the world, measuring the concentrations of aerosol particles in the atmosphere, along with the concentrations of plant gases, the temperature, and reanalysis estimates for the height of the boundary layer, which turned out to be a key variable. The boundary layer refers to the layer of air closest to the Earth, in which gases and particles mix effectively. The height of that layer changes with weather. Paasonen says, “One of the reasons that this phenomenon was not discovered earlier was because these estimates for boundary layer height are very difficult to do. Only recently have the reanalysis estimates been improved to where they can be taken as representative of reality.”

However, is not pointed out in either the article, nor the interview, that as currently estimates of "climate sensitivity" do not include this negative feedback; in order for Global Circulation Models, GCM's including this negative feedback to match historical records they will need to utilize higher effective "climate sensitivity" values; which should resulting in higher projections of global temperature increase, if plant growth/activity does not keep path with the rate of future green house gas, GHC, emissions.

This article opens with the statement that: "Rahmstorf et al’s (2012) conclusion that observed climate change is comparable to projections, and in some cases exceeds projections, allows further inferences if we can quantify changing climate forcings and compare those with projections." They then present the first attached image that is very similar to the image that I presented in my first post in this thread; which shows that anthropogenic CO2 emissions are exceeding the IPCC projected anthropogenic emissions. This would seem to support some of my previously stated concerns.

Hansen et al 2013 then present the next attached image that shows the change in CO2 with both the change in global mean temperature and the Nino Index. This figure indicates that since at least 2000 the rate of increase of atmospheric CO2 content has not increase at the same rate as the anthropogenic CO2 emissions, apparently partially due to the El Nino "hiatus period" observed since 2000 as this "hiatus period" apparently promotes terrestrial biological growth that has been absorbing CO2 at a rate faster than once feared.

The fact that the environment has recently absorbing CO2 at a faster rate than the growth of anthropogenic CO2 emissions is illustrated by Hansen et al 2013's third attached image showing that the airborne fraction of emissions from about 60% to about 50%. Hansen et al 2013 attribute this increase in absorption not only to the "hiatus period" but also to that fact that China and India have accounted for most of the increase in anthropogenic CO2 emissions due to increase burning of coal, which generates more aerosols and particulates; which apparently has promoted biological growth both by creating diffused sunlight that plants can absorb more efficiently and due to the distribution of nitrogen in the particulates that acts like a fertilizer. Hansen et al 2013 then show that methane emissions have increased recently (as I have also noted recently).

Hansen et al 2013 then present the last attached figure which shows that the radiative forcing from GHG emissions have fallen well below the IPCC projections since at least 2000, apparently not only due to high rate of environmental absorption of CO2, but also due to the unexpectedly high rate of reflection of solar irradiance due to the high levels of aerosols and particulates associated with the coal burning in China, India and general emissions in Africa. To wit Hansen et al 2013 state: "If greenhouse gases were the only climate forcing, we would be tempted to infer from Rahmstorf’s conclusion (that actual climate change has exceeded IPCC projections) and our conclusion (that actual greenhouse gas forcings are slightly smaller than IPCC scenarios) that actual climate sensitivity is on the high side of what has generally been assumed. Although that may be a valid inference, the evidence is weakened by the fact that other climate forcings are not negligible in comparison to the greenhouse gases and must be accounted for." These other not negligible climate forcings include: increase solar irradiance due to the solar cycle, increase black carbon emissions and activity, and uncertainty about the influence of aerosols on the reflection of solar irradiance. Furthermore, while Hansen et al 2013 did not specifically cite it, nevertheless, the "hiatus period" apparently has also temporarily increased ocean heat uptake since at least 2000.

Hansen et al 2013 note that the earth is currently in a "Faustian bargain" situation where an end to the "hiatus period" and - or a decrease in air pollution emissions in Asia and Africa (either due to public demands or a change to shale gas from coal) both would increase the airborne fraction of CO2 in the atmosphere compared to emissions and would decrease the reflection of solar irradiance due to air pollution aerosols; which could result in future dramatic increases in mean global temperature increases. It would appear that our current "Faustian bargain" many not have a happy ending.

To supplement the previous information that I provided on Black Carbon, I present the following information from the Environmental and Energy Study Institute:

"Black carbon, or soot, is a form of particulate matter (PM) and, therefore, behaves much differently than GHGs. It does not become well-mixed in the atmosphere; particles remain suspended in the air until they settle back on the surface, become washed out by rain, or contribute to cloud formation. The average atmospheric lifetime of a single soot particle is only two or three weeks. As a dark mass, black carbon particles absorb abundant amounts of energy, trapping heat and warming the climate. Like methane, black carbon warms the climate more intensely than CO2 over a short time frame, but to greater extremes. Despite lasting in the atmosphere for less than one month, one ton of black carbon has a warming effect equal to 1,000-2,000 tons of CO2 over a 100-year period. Over a 20-year span, one ton of black carbon likely has an impact greater than 4,000 tons of CO2. Black carbon’s radiative forcing is an area of active research. The Intergovernmental Panel on Climate Change (IPCC) lists its value at 0.44 W/m2, but this is based on older models. A widely-cited 2008 study approximates black carbon’s radiative forcing at 0.9 W/m2 – a warming effect equal to 54 percent of CO2. A 2013 study estimated this value to be 1.1 W/m2. While black carbon radiative forcing estimates all have large ranges of uncertainty, there is growing evidence that black carbon has the second largest warming impact of all climate pollutants. Black carbon is co-emitted with other forms of PM, some of which have significant cooling impacts that offset a portion of black carbon’s full warming impact. The emissions ratio of black carbon to cooling particulates varies by source, giving some mitigation strategies (i.e. cleaner diesel engines) a greater potential climate impact. All PM reduction strategies, however, provide important public health benefits.

Black carbon does not warm only the atmosphere. Some emissions settle on snow, glaciers, and sea ice, darkening their surfaces. This significantly reduces the reflectivity, or albedo, of the surface, causing it to absorb more solar energy and accelerating ice melt. The globally-averaged effect of this process is estimated at 0.1 W/m2, but in reality, this impact is concentrated at much higher rates in a few very climate-sensitive regions, including the Arctic and the Himalayas. Additionally, black carbon is a primary contributor to both indoor and outdoor air pollution, which together cause more than three million deaths annually.

Black carbon emissions are the result of incomplete combustion of biomass or fossil fuels. Closed combustion makes up 59 percent of emissions; open burning is responsible for the rest. Major sources of black carbon include inefficient biomass cooking stoves, diesel and two-stroke engines, and open-air-vented coal furnaces. "

I am traveling for the rest of this week, so at best I will make brief posts, such as this to note that the attached image indicates that methane emissions in the continental USA are up 9% from US gas fields, as indicated in the quote below:

"Real-world observations have repeatedly made clear that industrial methane emissions are larger than we think. See “Bridge To Nowhere? NOAA Confirms High Methane Leakage Rate Up To 9% From Gas Fields, Gutting Climate Benefit.” Here’s yet another study. Methane data collected from Florida to California in 2010. Both the spatial average and the raw data show the highest levels were in the East Texas area, decreasing westward and eastward."

Sidd, there is a decades long trend of heating at depths greater than 2000m that goes along with the heating in waters < 2000 meters. Warmer water doesn't hold oxygen as well as colder water so the processes affecting ventilation of the deep ocean are changing. The processes driving the fluctuation between surface heating( < 300 m ) and deep water heating ( 700-2000m ) for the decade you graphed would be interesting to better understand. It would seem to me that mixing between the bottom waters that are warming and freshening and the waters above them that are also warming would make dipycnal mixing and upwelling of those waters easier. The Antarctic bottom waters contain more oxygen than the older deep waters above them but as bottom water slows and warms this will mean less oxygen in the deep waters that mix and complete meridional flows. The Kracken will come up for some air.

The first images shows: "Researchers for the first time mapped the extent and frequency of understory fires across a study area (green) spanning 1.2 million square miles (3 million square kilometers) in the southern Amazon forest. Fires were widespread across the forest frontier during the study period from 1999-2010. Recurrent fires, however, are concentrated in areas favored by the confluence of climate conditions suitable for burning and ignition sources from humans. Image credit: NASA's Earth Observatory"

The second images shows: "Dials indicate regions in the southern Amazon forest predicted to have below-average fire activity (green) and above-average activity (orange and red) during the 2013 dry season, relative to the 2001-2012 mean. Credit: UC Irvine." The information from this website indicates that climate change is increasing this risk of understory fires in the Amazon.

The following quote from the IEA indicates the difficulty with limiting anthropogenic radiative forcing below the businss as usual, BAU, cases:

"“Climate change has quite frankly slipped to the back burner of policy priorities. But the problem is not going away – quite the opposite,” IEA Executive Director Maria van der Hoeven said in London at the launch of a World Energy Outlook Special Report, Redrawing the Energy-Climate Map, which highlights the need for intensive action before 2020.

Noting that the energy sector accounts for around two-thirds of global greenhouse-gas emissions, she added: “This report shows that the path we are currently on is more likely to result in a temperature increase of between 3.6 °C and 5.3 °C but also finds that much more can be done to tackle energy-sector emissions without jeopardising economic growth, an important concern for many governments.”

New estimates for global energy-related carbon dioxide (CO2) emissions in 2012 reveal a 1.4% increase, reaching a record high of 31.6 gigatonnes (Gt), but also mask significant regional differences. In the United States, a switch from coal to gas in power generation helped reduce emissions by 200 million tonnes (Mt), bringing them back to the level of the mid 1990s. China experienced the largest growth in CO2 emissions (300 Mt), but the increase was one of the lowest it has seen in a decade, driven by the deployment of renewables and improvements in energy intensity. Despite increased coal use in some countries, emissions in Europe declined by 50 Mt. Emissions in Japan increased by 70 Mt."

Considering the fractured state of the Arctic Sea Ice, I thought that it would be appropriate to post the attached Solar Irradiance curves from March 21 to June 12 2013, indicating the the solar irradiance is relatively high at the moment and that if there is significant ice area loss from the Arctic Ocean then the associated loss of albedo could help to accelerate global warming and thus associated ice mass loss from the WAIS and the AIS.

The following summary (and associated image) about a wildfire in Alaska (from the indicated website), and a record-setting potential for more fires across boreal spruce forests and tundra landscapes, has many people on edge, given the high impact of the 2007 Alaskan wildfire:http://www.sciencecodex.com/wilfire_smoke_over_alaska-114516"On June 19, 2013, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured this image of smoke from wildfires burning in western Alaska. The smoke was moving west over Norton Sound. (The center of the image is roughly 163° West and 62° North.) Red outlines indicate hot spots where MODIS detected unusually warm surface temperatures associated with fire.According to an advisory released by the Alaska Interagency Coordination Center, record heat and dry fuels have produced record-setting fire potential across boreal spruce forests and tundra landscapes. The heat wave is the product of an intense ridge of high pressure over the state."

If the current high surface temperatures continue in Alaska and Siberia then wildfires in the tundra could become a significant forcing for global warming due to arctic amplification.

"Arctic vegetation spread could boost climate changeByBill SteeleChanges in Arctic vegetation due to climate change have probably been underestimated, according to a new computer analysis which shows that tree and shrub cover in the region will increase more than previously expected, accelerating climate change and possible adverse effects on wildlife.“Such widespread redistribution of Arctic vegetation would have impacts that reverberate through the global ecosystem,” said Richard Pearson, a research scientist at the American Museum of Natural History’s Center for Biodiversity and Conservation and lead author of the study. Pearson, working with scientists at Woods Hole Research Center in Falmouth, Mass., called in computer scientists with access to the high-performance computing facilities at Cornell’s Institute for Computational Sustainability (ICS) and AT&T Labs to conduct the analysis. The results appeared March 31 in the journal Nature Climate Change.The overall prediction is that woody cover will increase by as much as 52 percent by the 2050s. With trees and shrubs hiding the snow, less heat will be reflected. Tree growth will expand hundreds of kilometers north of the present tree line in Siberia, while woody shrubs will overrun grasses in Alaska. The vegetation that is displaced will have no room to move farther north, so some habitats may disappear, along with the birds and animals that depend on them. The vegetation also will transpire more water vapor, which acts as a greenhouse gas.Previous predictions have been based on computer simulations of the biological processes of plant growth in response to changes in temperature. The new approach analyzes what has actually been happening up to now and projects that into the future with unprecedented detail. The computer divided maps into thousands of cells 4.5 kilometers square, separately computing the outcome for each one.The researchers fed in detailed data on how vegetation has changed from 1950 to 2010 in response to global warming. Juggling up to half a million variables, the computer learned how the distribution of vegetation correlates with climate, then used projections of future climate to compute trends for the future. Predictions were made for several different types of grasses, shrubs and trees; each plant group has a climatic “niche” – a set of conditions that favors its growth. “Vegetation distribution shifts will result in an overall positive feedback to climate that is likely to cause greater warming than has previously been predicted,” the researchers said in their paper. Thick tree cover also may alter the ecosystem by depriving low-lying plants of sunlight, they added. Further along, the researchers said, there may be impacts on human society.ICS operates a state-of-the-art parallel computer cluster of 600 processors, dedicated to research on issues of sustainability such as land use, climate modeling and the interaction of species with the environment, all problems involving complex computing with many variables. Running many calculations in parallel can vastly reduce the time needed to analyze these problems, said Carla Gomes, professor of computing and information science and director of ICS.Different computer models were used at AT&T and Cornell, with good agreement on the results. The models were more than 80 percent correct, said Cornell graduate student Theo Damoulas, who designed the Cornell model.The research was supported by the National Science Foundation, which also funded the creation of ICS and its computing facility."

The caption for the attached image is: Distributions of vegetation in Siberia, Alaska and Western Canada today, left, and as predicted for 2050 by computer models. Replacing grasses with tree cover and woody shrubs (green, blue and purple) will decrease the reflection of sunlight and feed back to increase global warming.

Abstract:"Biomass burning is one of the largest sources of carbonaceous aerosols in the atmosphere, significantly affecting earth’s radiation budget and climate. Tar balls, abundant in biomass burning smoke, absorb sunlight and have highly variable optical properties, typically not accounted for in climate models. Here we analyse single biomass burning particles from the Las Conchas fire (New Mexico, 2011) using electron microscopy. We show that the relative abundance of tar balls (80%) is 10 times greater than soot particles (8%). We also report two distinct types of tar balls; one less oxidized than the other. Furthermore, the mixing of soot particles with other material affects their optical, chemical and physical properties. We quantify the morphology of soot particles and classify them into four categories: ~50% are embedded (heavily coated), ~34% are partly coated, ~12% have inclusions and~4% are bare. Inclusion of these observations should improve climate model performances."

The Sanderson et al 2011 study considers what they call an all coal scenario to represent the highest emission scenario that they were willing to consider believable; however, I suggest that here that this "all-coal" scenario could serve as a proxy for a more likely scenario where before the end of the century most of the world is using equivalent percentages of shale gas (including methane leakage) that that considered by Sanderson et al 2011 for the all-coal scenario.

With this in mind, I post the first attached image of Sanderson et al 2011 emission scenarios, and the second attached image that shows the associated projected mean global surface temperatures at the 50% CL levels. Next (for convenience) I re-post the third image showing the confidence ranges for the SRES and RCP scenarios to give the readers a feeling for over confidence levels. I believe that this information indicates that the RCP 8.5 95%CL scenario that I have been most frequently citing could also be non-conservative from a public safety point of view, if the world were to become dependent on shale gas without controlling methane leakage.

With regard to my last post if shale gas is allowed to leak while being collected it can have a greenhouse gas potential equal to, or exceeding, that of coal. The first attached image shows a table of the countries with the largest amounts of technically recoverable shale gas (note EU countries are relatively small but taken together they have a large amount of shale gas reserves). The second image compares the projected production rates for the countries (China and USA) with the largest shale gas reserves. The indicated recoverable reserves of shale gas are large, and if agressively developed could drive GHG emissions well above RCP 8.5 95% CL.

"The world's population could reach 11 billion by the year 2100, according to a new statistical analysis.That represents 800 million more people than was forecast in 2011. Most of that increase comes because birth rates in Africa haven't dropped as fast as projected."

"The fertility decline in Africa has slowed down or stalled to a larger extent than we previously predicted, and as a result the African population will go up," said study co-author Adrian Raftery, a statistician at the University of Washington, in a statement."

"Right now, Africa's population stands at 1.1 billion, but that is expected to increase four-fold, to 4.2 billion, by 2100."

"The new analysis used a more sophisticated method for estimating life expectancy, updated fertility forecasting methods and new population data.The model predicts that the population will likely reach between 9 billion and 13 billion by 2100. By contrast, the U.N.'s population estimates assume the average birth rate may vary by up to 0.5 children per woman, which results in a large range for the world's population at the end of the century, between 7 billion and 17 billion."

Furthermore, food production currently contributes about 30% of all GHG emissions, and food production by 2100 is estimated to be between 2 to 3 times current levels both due to population growth and due to richer diets.

Therefore, it is becoming increasing likely the anthropogenic GHG emissions will exceed RCP 8.5 95% CL by the end of the century.

At the risk of being thought of as a Jeremiah (a cautionary haranguer), instead of a Pollyanna (a starry-eyed optimist); in-addition to citing the risks of increased future radiative forcing from things like shale gas (see Reply 39), population growth and food production (see Reply 40); I would like to post the following two robot-related projections from: (A) Dave Evans, chief futurist at Cisco Systems, and Guido Jouret, chief technology officer for emerging technologies; and (B) a recent report on 20 Forecasts for 2013-2025 (see the following website: http://www.wfs.org/forecasts/):

(A) "Evans predicts that by 2038 there will be more robots than there are humans in the world. Many of them will be doing jobs now done by people."(B) "Robot development may soon dramatically accelerate thanks to new open-source hardware-sharing systems. Similar to open-source software for computers, this new robot-development platform allows participants to share their designs so that other developers can adapt or improve on them. By sharing hardware and software development, costs may plummet and innovation may skyrocket. For example, a caregiving robot that used to cost more than $350,000 to purchase may soon be available for under $25,000."

Thus I believe not only will the effort to both build and operate robots contribute more to GHG emissions than previously projected by the IPCC; and that other risks such as possible wars and the effort required to deal with the consequences of climate change, will also up anthropogenic GHG emission scenarios beyond what was previously envisioned by RCP 8.5.

The information in the article at the following link indicates that if we stay on a path at or above RCP 8.5 95%CL; then before the end of this century the amount of GHG absorbed by the environment will drop sufficiently to cause a "tipping point", where the environment begins to emit carbon into the atmosphere:

In addition to previously stated reasons that all of the SRES and RCP emission scenario may be too low (such as the growth of: shale gas, population, rate of reduction of GHG absorption, tar sands, growth of China's economy, etc); is the recent emergence of a deeply interconnected global economy that has a large reserve of capital, access to cheap labor anywhere in the world; access to planet-wide communication systems and transport systems, access to growing consumer markets, and that is less subject to the limits of national regulation/manipulation. This global economy shifts resources rapidly to exploit windows of opportunity around the would, aided by technology (cellphones, 3D printers etc) that allow capital to flow particularly to the third world (Africa, Southeast Asia etc) to simulate growth and consumption more rapidly than the developers of the SRES and RCP scenarios had assumed (e.g. the rapid growth of China was not expected to occur so fast). This very extractive global economic system will be difficult to slow, which is the main reason why we are already exceeding the RCP 8.5 95% CL scenario dispite the Kyoto Protocol's and the IPCC's limited efforts; and there is know reason to assume that in the future the world economy will not be able to exceed RCP 8.5 95% CL.

"The wilds of Alaska have been categorized under the largest wildfires ever in the last decade in US. It accounts for record-breaking blazes witnessed from a long time. Here, half a million acres of land blackened in one moment.Speaking on the severity of wildfires, University of Illinois plant biology Prof. Feng Sheng Hu said, "In the last few decades we have seen this extreme combination of high severity and high frequency".This fact has been unveiled by a new study. The study that has been published in the Proceedings of the National Academy of Sciences studied charcoal sediment corings from 14 Yukon Flats lakes. Hu and the co-authors reconstructed the fire to understand the history of the region.This is not the only place that has come across wildfires. There is an extension of Alaska called as North America's boreal forests, the Far North belt of spruce and fir trees that have been classified under the worst wildfires ever.According to the study, changed climatic conditions can be really severe. This could promote wildfire to a great extent where the forests can eventually be converted into deciduous woodlands of aspen and birch, said researchers.So, after the study they concluded that the climate change had a great role to play in Alaska boreal forest wildfires."

"AbstractPolar surface temperatures are expected to warm 2-3 times faster than the global mean surface temperature; a phenomenon referred to as polar warming amplification. Therefore, understanding individual process contributions to the polar warming is critical to understanding global climate sensitivity. The coupled feedback response analysis method (CFRAM) is applied to decompose the annual and zonal mean, vertical temperature response within a transient 1% yr-1 CO2 increase simulation of the NCAR CCSM4 into individual radiative and non radiative climate feedback process contributions. The total transient annual mean polar warming amplification (amplification factor) at the time of CO2 doubling is +2.12 K (2.3) and +0.94 K (1.6) in the northern and southern hemisphere, respectively. Surface albedo feedback is the largest contributor to the annual mean polar warming amplification accounting for +1.82 K and +1.04 K in the northern and southern hemisphere, respectively. Net cloud feedback is found to be the second largest contributor to polar warming amplification (about +0.38 K in both hemispheres) and is driven by the enhanced downward longwave radiation to the surface resulting from increases in low polar water cloud. The external forcing and atmospheric dynamic transport also contribute positively to polar warming amplification: +0.29 K and +0.32 K, respectively. Water vapor feedback contributes negatively to polar warming amplification because its induced surface warming is stronger in low latitudes. Ocean heat transport storage and surface turbulent flux feedbacks also contribute negatively to polar warming amplification. Ocean heat transport and storage terms play an important role in reducing the warming over the Southern Ocean and Northern Atlantic Ocean."

The following article is from the "Climate Progress" website; and while this plan by China to spend $275 Billion to combat air pollution, is very good for the health of the Chinese; it also needs to be recognized that this action will increase the rate of global warming as all of that air pollution acts as a negative feedback to global warming (and cleaning the air pollution up will cause future global temperatures to rise; which will contribute to accelerated ice mass loss in Antarctica):

China’s air pollution levels have reached dire levels, even breaking the upper limits of the Air Quality Index earlier this year. In a sign the government is serious about tackling this crisis, The China Daily announced Thursday that China will spend $275 billion over the next five years to reduce emissions and launch anti-pollution programs. The funds, which exceed the total economic output of Hong Kong last year, will target emissions in the densely populated area surrounding Beijing, where residents have suffered through off-the-charts pollution and all its accompanying illnesses. Air pollution caused more than 1.2 million premature deaths in China in just one year, while some Beijing schools are building air-purified domes over playgrounds so children can play “outside” safely. Anti-pollution protests have grown more and more prevalent all over the country.These unsustainable conditions are directly linked to China’s rapid industrialization. Most of Beijing’s pollution stems from factories and power plants outside the city. China’s coal production has tripled in the past ten years as the nation’s energy consumption has exploded. The Chinese government, up til this year, has aggressively encouraged economic growth at the expense of the environment and public health.But now that the environmental repercussions cannot be ignored, the government has done a hard about-face. New promised anti-pollution measures include speedy installation of pollution control equipment on coal-fuelled refineries, restrictions on high energy consumption industries like steel, cement, and glass, and use legal action to force industries to upgrade their emissions standards."

In the ASIB, Allen W. McDonnell posted the following links to information raising the possibility that the current three atmospheric cell configuration (Hadley, Ferrel and Polar Cells) shown in the first attached image (as a side point discussed in the "Methane" thread, note the convex geopotential height topology over the Arctic and the concave geopotential height topology over the Antarctic), could be transformed into the single Hadley Cell configuration shown in the second attached image.

that the Northern Hemispheric (NH) atmosphere is more susceptible to such a three-cell to one-cell transition; with sufficient forcing the Southern Hemispheric (SH) atmosphere could make the same transition sometime later (decades, or longer). Nevertheless, in either a one-cell NH and three-cell SH case, or a one-cell NH and one-cell SH case, there would likely be more telecommunication of heat to Antarctica (possibly substantially in the one-cell NH / one-cell SH case). While nothing that I have posted in the Antarctic folder assumes such an event; it is clear to me that should such an atmospheric transition occur, ASLR could continue well after 2100 with significant SLR contribution coming from EAIS after 2100 (which would make my SLR curves posted in the "Philosophical" thread non-conservative from a safety point of view.

The following two links connect to articles indicating that earthquakes can trigger the release of sufficient quantities of marine methane that climate change researchers should include this as a meaningful source of GHG.

While the following article addresses paleo climates; nevertheless it's finding of possible abrupt changes from cool to warm atmospheric patterns could contribute to increase the calculated risk of abrupt ice mass loss from the WAIS this century:

"AbstractThe coupled climate dynamics underlying large, rapid, and potentially irreversible changes in ice cover are studied. A global atmosphere–ocean–sea ice general circulation model with idealized aquaplanet geometry is forced by gradual multi-millennial variations in solar luminosity. The model traverses a hysteresis loop between warm ice-free conditions and cold glacial conditions in response to ±5 W m−2 variations in global, annual-mean insolation. Comparison of several model configurations confirms the importance of polar ocean processes in setting the sensitivity and time scales of the transitions. A “sawtooth” character is found with faster warming and slower cooling, reflecting the opposing effects of surface heating and cooling on upper-ocean buoyancy and, thus, effective heat capacity. The transition from a glacial to warm, equable climate occurs in about 200 years.In contrast to the “freshwater hosing” scenario, transitions are driven by radiative forcing and sea ice feedbacks. The ocean circulation, and notably the meridional overturning circulation (MOC), does not drive the climate change. The MOC (and associated heat transport) collapses poleward of the advancing ice edge, but this is a purely passive response to cooling and ice expansion. The MOC does, however, play a key role in setting the time scales of the transition and contributes to the asymmetry between warming and cooling."